Will these be better

When i brought my 2001 WR426 Australian modle new i got anouther set of jets and i was wondering if i should try them I dont know what the jets are called but here are the numbers 1 with a end for a flathead screwdriver is some symbol 38 and the other 2 thay are shorter they are symbol 170 and a symbol 160 i dont know what are in my bike from factory but these came with the bike thay where in a sealed packet ind i dont know what they are for i have removed the airbix lid and have a FMF powercore 1V2 exhaust i just want to know what these jets will do because i forgot i had them and i am now 2 and a half turns out on the air fule is that to far?

Yours sincearly Pete..


The one with the screwdriver head and the emulsifier tube on the business end marked 38 is the pilot jet. The two shorter 6mm hex jets are main jets.

I believe the stock pilot jet on your bike was a 42. You are running 2 1/2 turns out on the pilot fuel screw which is on the far end but not too far. If that seems right just leave it. If you needed to go further out, you would replace the pilot with a bigger one and turn the fuel screw back in.

The two main jets are bigger (richer) and smaller (leaner) than the stock. If you don't have a rich/lean problem at wide open throttle, stay where you are.


Thats the problem i dont know if im rich or lean at wide open my bike started breaking down the other day at full throtle with a fair few revs it felt like the chain was jumping but thats not it but it only dus it in 5th gear i think it might be the plug (but i was hoping to get mort than 1000ks out of one) but it just started doin it i hadent made any ajustments

And before you ask its not the rev limeter

Yours sincearly Pete

Winter is coming on down there isn't it? I have been learning about jetting the hard way thru trial and error. I had no idea what a rich or lean bike felt like.

I think I now know what a lean bike feels like. My mid throttle would miss, pop and backfire and feel like the chain was skipping. When I would go up into the mountains that sensation would almost stop. So I figure my bike was actually too lean. I have since richened the bike and it runs pretty good right now.

I would try going to a richer Main Jet. Is this correct? Taffy, Anyone? Cause if I am wrong than I am giving up this whole jetting mess.

I just got through posting on the 250F forum under the Subject: If you have never jetted but think you need to... It has the basics of jetting in it. I'm no expert but have learned a little.

Pete, I can't explain why it would only happen in fifth gear. When a plug is lightly fouled, it will often run fine up to a certain throttle position or RPM (varies with level of fouling) and then act very lean (pop, backfire, and stop running for up to a second at a time) and then run fine when at low RPMs. Plug is a good guess and cheap and easy to try.

Dan, you're spot on. I assume you richened up the pilot and/or the needle. Do both. Yes, it probably needs a larger main also. JD has a jetting spreadsheet that easily lets you visualize jetting changes if you're willing to spend $20. If not try the plug test or just try the next larger size. The post in the 250F forum may help but its pretty basic. For more advanced jetting, the Jetting Q's on this forum is amazing but confusing.

Whoops, just re-read your post. If it only had popping symptoms at mid-throttle, enrichening with the needle clip (lowering clip which raises needle) is probably all that's needed for basic jetting.


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